1. Field of the Invention
This invention relates to a smoke detecting apparatus for a fire alarm having a smoke chamber in which a light emitting lamp like a xenon lamp and a light receiving element are provided. Light from the light emitting lamp is received by the light receiving element, and the density of smoke caused by a fire is detected in accordance with an output signal emitted from the light receiving element.
2. Description of the Related Art
In a conventional smoke detecting apparatus in which the density of smoke introduced into a smoke chamber is detected in accordance with an output signal of a light receiving element which receives light emitted from a xenon lamp, the level of the output signal of the light receiving element is gradually lowered as the light emission efficiency of the xenon lamp and the light reception efficiency of the light receiving element are deteriorated, or as the xenon lamp and the light receiving element are contaminated, as a result of a change which takes place over a period of time.
This lowering of the output signal level of the light receiving element results in the smoke detecting apparatus becoming incapable of operating normally. In such a case, a warning, e.g., an alarm, is given to indicate the abnormal condition of the xenon lamp or the light receiving element. After a person has noticed this warning and maintenance work such as replacement and cleaning of the xenon lamp, the light receiving element, etc., has been performed, the smoke detecting apparatus is capable of operating normally again.
In the above-described conventional technique, the maintenance work such as the replacement and cleaning of the xenon lamp, the light receiving element, etc., must be executed in order that the smoke detecting apparatus may operate normally again. However, this maintenance work such as the replacement and cleaning of the xenon lamp, the light receiving element, etc., is not the kind of work that any person can perform. In particular, a high-sensitivity smoke detector is usually sent to a service plant for maintenance.
Further, in the case of such a high-sensitivity smoke detector, periodical maintenance is executed thereon, for example, every two years, at which time the xenon lamp is replaced with a new one. In this case, the smoke detecting apparatus needing maintenance is detached from its location, and an alternate normal smoke detecting apparatus is installed in its place. After the former detecting apparatus has finished undergoing the requisite maintenance at the service plant, it is installed at its location again, the alternate one being taken away. In this way, the continuity of the smoke detecting operation is maintained.
The above-described conventional smoke detecting apparatus, however, has a problem in that if there is no alternate smoke detecting apparatus at hand at the time that the level of the output signal of the light receiving element is lowered, the continuity of the smoke detecting operation has to be interrupted. Furthermore, the normal smoke detecting operation cannot be started again until an alternate smoke detecting apparatus has been installed. This problem is also experienced when a light emitting lamp other than a xenon lamp is used.